57-1 Calibrating Miocene Earth System Change and Time Scales Requires High-Precision Geochronology in a Stratigraphic Context

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part II

Presenting Author:

Jennifer Kasbohm

Authors:

Kasbohm, Jennifer Jean¹, Schoene, Blair², Mark, Darren³, Reidel, Stephen P.⁴, Montanari, Alessandro⁵, Thomas, Ellen⁶, Hull, Pincelli M.⁷

(1) Carnegie Science, Washington, DC, USA, (2) Princeton University, Princeton, NJ, USA, (3) Isotope Geosciences Unit, Scottish Universities Environmental Resource Center, University of Glasgow, East Kilbride, United Kingdom; Department of Earth and Environmental Science, University of St Andrews, St Andrews, United Kingdom, (4) (Retired), Pacific Northwest National Laboratory, Richland, WA, USA, (5) Osservatorio Geologico di Coldigioco, Apiro, Italy, (6) Wesleyan/Yale, New Haven, CT, USA, (7) Yale University, New Haven, CT, USA,

Abstract:

Understanding the climatic and biotic changes experienced by the Earth system during the Miocene requires accurate and precise chronologies that allow for a detailed alignment and integration of proxy records. High-precision U-Pb zircon geochronology through chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) routinely yields ages with precision >0.1%. Knowledge of a sample’s stratigraphic position can be incorporated into age models to further reduce age uncertainties, and these age models can refine estimates for bio- and magnetostratigraphic events used to calibrate the Geologic Time Scale.

Here we present results from three studies that utilized high-precision U-Pb CA-ID-TIMS zircon geochronology obtained within a stratigraphic context. First, in the Lower Miocene Bisciaro Formation (Gubbio, Italy), U-Pb zircon ages from four ashes show that deposition occurred between ~22.3 and 20.1 Ma, rather than 22-17 Ma (Kasbohm et al., 2021). This new age model can recalibrate paleoclimate studies based on Bisciaro sediments, and revises chronologies for foraminiferal occurrences cited in Geologic Time Scale 2020. Next, large igneous province volcanism of the Columbia River Basalt Group (CRBG) has been suggested to play a causal role in elevated global temperatures and atmospheric carbon dioxide levels of the Miocene Climate Optimum (MCO). We present 23 high-precision ages, using CA-ID-TIMS U-Pb on zircon and multi-collector ⁴⁰Ar/³⁹Ar on basaltic groundmass, to provide a detailed dual-chronometer timeline for CRBG eruptions. We use both sets of new ages and precise stratigraphic positions of our samples in an integrated Markov Chain Monte Carlo model, which yields long-term emplacement rates for main-phase CRBG volcanism of 0.2-0.9 km³/yr and ages for all magnetic field reversals during the main phase of CRBG emplacement (Kasbohm & Schoene, 2018; Kasbohm et al., 2023). Finally, we use zircon geochronology to target the duration of the MCO from volcanic ashes at Ocean Drilling Program Site 1000 (Nicaragua Rise). We place these ages within a framework to address incomplete core recovery and use them to calibrate a high-resolution bulk carbonate δ¹³C and δ¹⁸O record. Our work shows that CRBG emplacement was coincident with the interval of greatest sustained MCO warmth at Site 1000 (Kasbohm et al., 2024). However, if the CRBG were the primary driver of the MCO, our chronology may allow for outgassing preceding volcanism as a major source of CO₂.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9909

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